Generally, a motor includes two end-plates provided at both ends of a core which is configured with a plurality of laminations. The core is sandwiched by the two end-plates in an axial direction of a shaft of a motor, or in a stacking direction where the plurality of the laminations are stacked. Generally, when current is supplied to a coil, a magnetic flux has to be generated within the motor only in a circumferential direction of the core. Generally, a nonmagnetic material is used for each of the two end-plate, which is provided to the motor in an axial direction of a shaft. Further, generally, each of the two end-plates is formed in a doughnut shaped plate by stamping out a long-shaped nonmagnetic material through a press process.
In JP2005304177A, the nonmagnetic material is used only for certain sites necessary, for example, the nonmagnetic material is used for a portion of an end-plate contacts a magnet or a part of a core having a plurality of laminations in order to reduce an amount of the nonmagnetic material used for the end-plate. In this publication, two end-plates are provided to the motor in order to sandwich the core. Additionally, in JP2005304117A, surfaces of each of the two end-plates are formed to be flat so that the each of the two end-plates contacts both ends of the core on its flat surfaces.
Generally, the end-plates are formed in a ring-shape by stamping out a long plate through the press process. However, forming the end-plates in the ring shape by stamping out the long plate leaves the rest of the long plate as waste materials. Therefore, in general, a large amount of the waste materials are created when the long plate is stamped out to form the end-plates.
Generally, the nonmagnetic material is more expensive than a magnetic material. In a process where the end-plates are formed by stamping out the long plate, the rest of the long plate used is discarded as the waste materials. Hence, a general process of stamping out a long plate made of the nonmagnetic material in order to form the end-plates decreases a level of a material yield and increases manufacturing costs of the end-plates.
On the other hand, in the way where each of the two end-plates is made of a combination of the nonmagnetic material and the magnetic material as disclosed in JP2005304177A, the amount of usage of the nonmagnetic material is reduced by using the nonmagnetic material to the certain sites of each of the two end-plates and by using the magnetic material to the rest of each of the two end-plate. In JP2005304177A, the nonmagnetic material is used, for example, for the portion of each of the two end-plates at which each of the two end-plates contacts the magnet or for the portion of each of the two end-plates at which each of the two end-plates contacts a part of the core including the plurality of laminations. However, in this configuration, additional processes for manufacturing the nonmagnetic end-plates and magnetic end-plates separately, and for combining the nonmagnetic end-plates and the magnetic end-plates may be needed. As a result, the manufacturing costs will be increased.
In general, the core including the plurality of the laminations and the end-plates are both formed by being stamped out through the press process. Therefore, warpage may be generated on the core and the end-plates, which results in insufficient contact between the end of the core and the end-plates.
In order to advance a performance of the motor, an external diameter of a rotor is enlarged or rotational speed of the rotor is increased. As a result, external force applied to the core of the rotor is also increased.
An outer portion of the core may be damaged if the core including the plurality of the laminations is not sufficiently press-fitted by means of the two end-plates from the both sides of the core.
A need thus exists to provide a motor which is not susceptible to the drawback mentioned above.